iPhone WiFi

I just recently got an iPhone 3gs, and have been having issues with very slow speeds when connected to my AirPort Extreme. My MacBook and my wife's PC work fantastic, but the speed on our iPhones in WiFi is terrible. We are very close to the base-station and get full WiFi bars so I know it's not a signal issue.

I read that it might be the firmware on the AirPort so I downgraded from 7.4.2 to 7.4.1 but that didn't seem to help. I have also read that the iPhone is a G only device and my other computers on the network are N, so I am wondering if this may have something to do with it.

I know that it can't be the phones because I took it to my Dad's house who has a cheap Linksys N router and the speeds were very fast when connected to his network.

In my utility's on my AirPort I have Radio Mode set to Automatic and Radio Channel set to Automatic. Should these be set to something different to take advantage of the dual range mode?

Anyone have any ideas or ran into something similar?